It is known to provide a current sensor that includes a magnetic sensing element such as a Hall element or a magnetoresistance (MR) element.
When a magnetic field is applied to the Hall element, a Hall voltage is generated across the Hall element. The Hall voltage changes proportional to strength of the applied magnetic field. In contrast, when an electric current. flows through a conductor such as a busbar, the magnetic field is induced around the conductor. The strength of the induced magnetic filed changes proportional to the amount of the current flowing through the conductor. Therefore, the current sensor can detect the current flowing through the conductor by detecting the Hall voltage.
However, when the current flowing through the conductor is small, the strength of the induced magnetic field is small. When the magnetic field is small, the Hall voltage does not change proportional to the magnetic field. Therefore, the current sensor may not accurately detect the current.
A current sensor disclosed in, for example, JP-H8-15321A or JP-H11-258275 includes a magnetic core that concentrates the magnetic field to increase the strength of the magnetic field applied to the magnetic sensing element.
As shown in FIG. 7, such a conventional current sensor includes a magnetic core 11 with a center opening through which a conductor 44 passes through and a magnetic sensing element 33 such as the Hall element. The magnetic core 11 has a pair of C-shaped core members 11a, 11b facing each other to provide gaps therebetween. The magnetic sensing element 33 is placed in one of the gaps.
When the current flows through the conductor 44, the magnetic field induced around the conductor 44. The magnetic core 11 concentrates the induced magnetic field and the concentrated magnetic field is applied to the magnetic sensing element 33 placed in one of the gaps. Thus, even when the current flowing through the conductor 44 is small, the conventional current sensor may accurately detect the small current.
However, the magnetic core 11 concentrates not only the induced magnetic field but also disturbance magnetic field such as geomagnetic field. As a result, the conventional current sensor may not accurately detect the current due to magnetic saturation.
To overcome the above problem, the current sensor disclosed in JP-H8-15321 includes a magnetic shield made of high permeability material. The magnetic core and the magnetic sensing element are wrapped by the magnetic shield to be protected from the geomagnetic field. However, the addition of the magnetic shield may increase size, weight, and cost of the current sensor.
The current sensor disclosed in JP H11-258275 includes a magnetic core having a low magnetic resistance portion. The disturbance magnetic field passes through the low magnetic resistance portion. Thus, the low magnetic resistance portion acts as a magnetic shield. In the current sensor, an U-shaped conductor is used as the current path to increase strength of the magnetic field detected by the magnetic sensing element. Therefore, whereas the current sensor may accurately detect a small current, the current sensor may not accurately detect a large current due to magnetic saturation.